Damascene processing is a method for forming metal lines on integrated circuits. It involves formation of inlaid metal lines in trenches and vias formed in a dielectric layer (inter metal dielectric). Damascene processing is often a preferred method because it requires fewer processing steps than other methods and offers a higher yield. It is also particularly well-suited to metals such as copper that cannot be readily patterned by plasma etching. In order to frame the context of this invention, a brief description of a Damascene process for forming a partially fabricated integrated circuit is described below.
A typical Damascene process flow begins with a dielectric into which recessed features have been etched. A diffusion barrier layer, followed by a metal layer are laid upon the dielectric. The metal layer is typically composed of copper or aluminum. The metal layer fills in the recessed features and forms conductive paths for the resulting IC device.
The barrier layer is important because metal ions from the conductive paths may otherwise diffuse into the silicon devise and the dielectric layer. Suitable materials for the diffusion barrier layer include tantalum, tantalum nitride, tungsten, titanium, titanium nitride, and the like. The barrier may be formed by a physical vapor deposition (PVD) process such as sputtering or a chemical vapor deposition (CVD) process. During the deposition process, etching of the diffusion barrier layer may be carried out on certain portions of the substrate to achieve optimal coverage.
Chemical-mechanical planarization (CMP) is employed to eliminate excess metal from the top of the dielectric and to create a flat top surface. CMP also removes the diffusion barrier layer on the field region.
This process can be repeated to create a multilayered IC device.